The idea that at least some of our actions are "up to us," that we can be the "authors of our own actions," and that they are not caused by external events, is perhaps the most ancient concept of "free will." Although the Romans had the same complex combination of free and will in their term (liberum arbitrium or libera voluntas), the Greeks had no such combination.

For the Greeks, and particularly for Aristotle, the term closest to the modern complex idea of free will, (which combines freedom and determination in an apparent internal contradiction) was ἐφ ἡμῖν - "on us" or "depends on us."

The original idea was thus supportive of accountability or moral responsibility, that our actions originate "within ourselves" (ἐν ἡμῖν), that as "agents" we are "causes," something that modern "semicompatibilists" like John Martin Fischer want to preserve even as they doubt freedom of the will.

Perhaps this is why Aristotle could not see any "problem" of free will.

Despite calling free will a "pseudo-problem" that could be resolved (or "dis-solved") by careful attention to the proper use of language, no analytic language philosopher appears to have resolved the one complex idea into two opposing but complementary concepts.

Analytic philosophers should note that John Locke was in the seventeenth century quite concerned that misuse of language lay behind the problem. In the Essay Concerning Human Understanding, Book II, Chapter XXI, Of Power, we find in section 14 that Locke calls the question of Freedom of the Will "unintelligible" (as had Thomas Hobbes before him). But for Locke, it is only because the adjective "free" applies to the agent, not to the will, which is determined by the mind, and which determines the action.

This seems to be Aristotle's view as well. Here is how he put it in Nicomachean Ethics, III, v, 6.

But if it is manifest that a man is the author of his own actions, and if we are unable to trace our conduct back to any other origins than those within ourselves, then actions of which the origins are within us (ἐν ἡμῖν), themselves depend upon us (ἐφ' ἡμῖν), and are voluntary. (Loeb translation.)

Aristotle had already argued against the atomists' necessity (Leucippus) and causal determinism (Democritus). He did not care for the atomists' atheistic dismissal of the gods, but he unequivocally endorsed chance, itself an atheistic idea flying in the face of the gods' foreknowledge, as the specific means of breaking the causal chain of determinism and necessity.

Aristotle had also treated a related problem that greatly concerned Epicurus, namely the idea that the current truth or falsity of a statement about the future entails the necessity of the future event. In de Interpretatione, IX, Aristotle argued that statements about future events have no truth value until the event does or does not occur. The future is thus open, to accidental chance for example. Epicurus connected this logical necessity to causal determinism, because, he said, a future event could not be fated and logically necessitated unless the causes of that event are already present. Note that neither Aristotle nor Epicurus are denying the principles of bivalence or non-contradiction. They both think these principles will apply once the future arrives.

The difference between Aristotle and Epicurus is then very slight as concerns the problem of free will. Aristotle never acknowledges the existence of a "free will problem." For him, it is transparent and obvious that our voluntary actions are "up to us." The determinism and necessity of the atomists is simply another impractical ideal, as inapplicable to the real world as the transcendental Ideas of his master Plato. And he was explicit that chance exists in the world.

Aristotle sees three causes or explanations for things that happen - necessity, chance, and a third thing (a tertium quid) in the agent-causality that he describes as "up to us."

For Epicurus, the atomic swerve was simply a means to deny the fatalistic future implied by determinism (and necessity). As the Epicurean Roman Lucretius explained the idea,

...if all motion is always one long chain, and new motion arises out of the old in order invariable, and if the first-beginnings do not make by swerving a beginning of motion such as to break the decrees of fate, that cause may not follow cause from infinity, whence comes this freedom in living creatures all over the earth
(De Rerum Natura, Book 2, lines 251-256)

Epicurus did not say the swerve was directly involved in decisions so as to make them random. His critics, ancient and modern, have claimed mistakenly that Epicurus did assume "one swerve - one decision." Some recent philosophers call this the "traditional interpretation" of Epicurean free will.

On the contrary, following Aristotle, Epicurus thought human agents have an autonomous ability to transcend the necessity and chance of some events. This special ability makes us morally responsible for our actions.

...some things happen of necessity (ἀνάγκη), others by chance (τύχη), others through our own agency (παρ’ ἡμᾶς).
...necessity destroys responsibility and chance is uncertain; whereas our own actions are autonomous, and it is to them that praise and blame naturally attach.

We know Epicurus' work largely from Lucretius and his friend Cicero. Lucretius describes Epicurus' idea of breaking the causal chain of determinism in De Rerum Natura. Indeed, without swerves, nothing would ever have been produced.

One further point in this matter I desire you to understand: that while the first bodies are being carried downwards by their own weight in a straight line through the void, at times quite uncertain and uncertain places, they swerve a little from their course, just so much as you might call a change of motion. For if they were not apt to incline, all would fall downwards like raindrops through the profound void, no collision would take place and no blow would be caused amongst the first-beginnings: thus nature would never have produced anything.

But if by chance anyone believes it to be possible that heavier elements, being carried more quickly straight through the void, fall from above or, the lighter, and so deal blows which can produce generative motions, he is astray and departs far from true reasoning. For whatever things fall through water and through fine air, these must speed their fall in accordance with their weights, because the body of water and the thin nature of air cannot delay each thing equally, but yield sooner overcome by the heavier ; but contrariwise empty void cannot offer any support to anything anywhere or at any time, but it must give way continually, as its nature demands : therefore they must all be carried with equal speed, although not of equal weight, through the unresisting void. So the heavier bodies will never be able to fall from above on the lighter, nor deal blows of themselves so as to produce the various motions by which nature carries on her processes. Therefore again and again I say, the bodies must incline a little; and not more than the least possible, or we shall seem to assume oblique movements, and thus be refuted by the facts. For this we see to be manifest and plain, that weights, as far as in them lies, cannot travel obliquely, when they drop straight from above, as far as one can perceive; but who is there who can perceive that they never swerve ever so little from the straight undeviating course?
(Lucretius, De Rerum Natura), book 2, lines 216-250, Loeb Classical Library, 113-115)

Lucretius may have associated the swerve more closely than did Epicurus himself with human freedom (libera) and with the will (voluntas) in this passage, where he identifies swerving (declinando) with "first-beginnings" of motions and describes our mind as swerving our motions wherever pleasure leads us.

Again, if all motion is always one long chain, and new motion arises out of the old in order invariable, and if the first-beginnings do not make by swerving a beginning of motion such as to break the decrees of fate, that cause may not follow cause from infinity, whence comes this free will (libera) in living creatures all over the earth, whence I say is this will (voluntas) wrested from the fates by which we proceed whither pleasure leads each, swerving also our motions not at fixed times and fixed places, but just where our mind has taken us? For undoubtedly it is his own will in each that begins these things, and from the will movements go rippling through the limbs.
(Lucretius, De Rerum Natura), book 2, lines 251-262, Loeb Classical Library, 115)

Note that the Loeb translators have made the common error of substituting "free will" for the first (free) part of Lucretius' description of the "libera voluntas." The second part is the will.

The original text says "whence comes this freedom (libera)," not "whence comes this free will." Epicurus and Lucretius need the swerve only to break the causal chains at some point earlier than our willed actions, so that our will can proceed "whither pleasure leads us" and "just where our mind takes us."

Nevertheless, both thinkers have been misinterpreted and criticized, starting in antiquity with the Stoics, notably Chrysippus, and later the Academic Skeptic Cicero, who in his De Fato and De Natura Deorum attacks the Epicureans and lampoons the idea of a "free will" based on random atomic motions.

Epicurus saw that if the atoms travelled downwards by their own weight; we should have no freedom of the will [Cicero says literally "nothing would be in our power"], since the motion of the atoms would be determined by necessity. He therefore invented a device to escape from determinism (the point had apparently escaped the notice of Democritus): he said that the atom while travelling vertically downward by the force of gravity makes a very slight swerve to one side. This defence discredits him more than if he had had to abandon his original position.
(Cicero, De Natura Deorum, Loeb Classical Library translation, v.40, p.67)

This "traditional interpretation" of a libertarian free will dependent on chance has been attacked for centuries as irrational and unintelligible.

This randomness objection is the second horn in the dilemma of the standard argument against free will. The first horn is the determinism objection and Epicurus was its discoverer.